The present invention relates generally to a method for controlling optical gain of an optical amplifier and, more particularly, to an optical power transient control scheme for erbium-doped fiber amplifiers (EDFA) used in long haul, high capacity dense wavelength division multiplexing optical networks.
EDFA amplifiers are used to compensate for the accumulated loss of various optical elements across an optical network and for the transmission loss across the optical fiber. These optical fiber amplifiers are operated at saturation such that the total optical output power is nearly constant independent of the number of wavelength channels present. If not controlled, the gain experienced by each channel will vary depending on the number of channels present.
Upon network reconfiguration, when wavelength channels are added or dropped or when the fiber is unexpectedly cut, sudden changes in the total input power are effected. Due to transient cross saturation in EDFA optical amplifiers, this sudden total power change induces power excursions on the surviving channels that can adversely affect the quality of service. Although this transient perturbation is generally slow in a single amplifier, the magnitude and speed of the transient power excursions accumulates as it passes through from stage to stage and grows quickly along a cascade of EDFA amplifiers. Surviving channel power variations can lead to unacceptable error bursts, due to exceeding the threshold for optical nonlinear effects, or, due to the receiver inability to handle such rapidly changing power levels.
Therefore, it is desirable to provide a method of electronically controlling the optical gain of an EDFA amplifier that will counteract the effect of sudden optical power change. This distributed control action across all of the optical amplifiers in the system together with optimized control performance will allow for very long chains of amplifiers in optical networks with dynamic wavelength provisioning. It is envisioned that the proposed control scheme will allow for very fast detection of transient changes in input optical power, as well as fast control settling time with minimal optical power degradation on the surviving channels. In addition, the proposed control scheme should be adaptable to specific optical network configurations and to handle unexpected add/drop in optical power.
In accordance with the present invention, an improved method is provided for electronically controlling an optical amplifier in an optical network. The method includes: receiving an optical signal into the optical amplifier; detecting input power of the optical signal entering the amplifier; supplying optical energy to the at least one doped fiber section associated with the optical amplifier using a laser source; detecting a sudden variation in the input power; and controlling the optical energy supplied by the laser source based only on the variation of the input power of the optical signal entering the amplifier.
In another aspect of the present invention, an alternative improved method is provided for electronically controlling the optical gain of an optical amplifier in an optical network. The method includes: receiving an optical signal into the optical amplifier; detecting output power of the optical signal at an output of a first doped fiber section, where the output of the first doped fiber section is connected to an input of a second doped fiber section; supplying optical energy to the second doped fiber section using a second laser source; and controlling the optical energy supplied by the second laser source based in part on the optical power detected at the output of the first doped fiber section.
For a more complete understanding of the invention, its objects and advantages, reference may be had to the following specification and to the accompanying drawings.